Wireless communication systems are under constant development and continuing efforts are made to increase the performance and efficiency within such systems. In view of this, a promising feature of future wireless communication systems comprises direct communication between user equipment in close proximity of each other, e.g. within a distance of a few tens or hundred meters. In future mixed networks, a user equipment may be in a direct device-to-device (D2D) mode in addition to a cellular mode. The D2D mode enables a number of potential gains over the traditional cellular technique, for example capacity gains, peak rate gains and latency gains.
Using 3GPP LTE (Long Term Evolution) as an example, the D2D communication is set forth as an underlay to LTE cellular network operation, wherein both the cellular communication and the D2D communication use the same communication resources. In the D2D mode the user equipment communicates directly with another user equipment, and in the cellular mode it communicates with the other user equipment via a base station in conventional manner.
FIG. 1 illustrates a mixed communication network 1, supporting user equipment being in the cellular mode as well as the D2D mode. In a typical scenario, a first user equipment 2 in D2D mode (in the following denoted first D2D user equipment 2) receives D2D configuration information from a base station 3. The configuration information comprises e.g. D2D transmit power and/or resource allocation.
A user equipment 4 in the cellular mode (in the following denoted cellular user equipment 4) experiences interference due to a D2D communication between the first and a second user equipment 5 in D2D mode (in the following denoted second D2D user equipment 5). The cellular user equipment 4 also receives D2D configuration information. The cellular user equipment 4 then receives a request from the base station 3 to measure on the D2D transmission between the first D2D user equipment 2 and the second D2D user equipment 5. In particular, the base station 3 requests the cellular user equipment 4 to monitor the control signaling between the first and second D2D user equipment 2, 5. The cellular user equipment 4 reports measurement results, e.g. interference channel information, to the base station 3. The base station 3 may then use the measurement results in various ways for increasing the overall performance in the communication network 1, e.g. for minimizing interference.
Knowledge about characteristics and parameters of channels between two communicating D2D user equipment and channels between the base station and the cellular user equipment is important for many reasons, e.g. for mode selection, scheduling, power control mechanisms, for minimizing intra-cell interference etc. For example, since the D2D users and the cellular user equipment communicate on the same set of resources (spectrum), interference measurements are important.
However, legacy user equipment, e.g. LTE Rel-8, 9 and 10, does not support the above described measurement and reporting. The measurement reports on the D2D communication would then be provided solely by user equipment supporting both modes. The legacy user equipment and the future user equipment supporting D2D as well as cellular communication will, as mentioned, share/use the same communication resources and measurement reports, e.g. cross channel measurements, from all user equipment would be valuable.